In communications systems, when two adjacent conductors carry signals, each conductor leaks a portion of its signal into the adjacent conductor, causing interference. Such interference is known as crosstalk. If crosstalk interference becomes too high for a signal, information in the signal may not be identifiable.
Digital Subscriber Line (DSL) services have been developed to operate using existing telephone copper wires providing users with relatively high-speed digital data communication services. As DSL signals are carried on copper wires, they are susceptible to crosstalk.
There are several classes of DSL services; some DSL services use frequencies that overlap with other DSL services. The many types of DSL service, Asymmetric Digital Subscriber Line (ADSL), Very High Speed Digital Subscriber Line (VDSL), High Speed Digital Subscriber Line (HDSL), etc., are referred to collectively as xDSL. Standards set for the different xDSL services specify power levels used to transmit their xDSL signals. The power level of a xDSL signal at a destination for that signal relative to the noise at the destination (i.e. the signal-to-noise ratio, or SNR) determines the transmission rate for that xDSL service; the higher the received SNR, the higher data throughput capacity of the transmission channel.
Standards set for the different xDSL services also specify frequencies used by their signals. Some xDSL services use frequencies that overlap with other xDSL services. As a general characteristic of transmitted signals, an xDSL signal attenuates as the signal propagates further away from the source. Higher frequency signals are more susceptible to this characteristic, attenuating more than lower frequency signals which have propagated the same distance. A low powered signal may be more susceptible to interference and crosstalk than a high powered signal. As such, xDSL services using higher frequencies must be deployed closer to the user to ensure an adequate power signal for transmissions. For example, some ADSL services, using lower frequencies than some VDSL services, have a maximum range of approximately 5.5 km from the source, while some VDSL services have a maximum range of approximately 1.5 km from the source. Therefore, there is an incentive to provide DSL services using higher frequency ranges from a source closer to the end user. The signals of these DSL services are provided from a cabinet, or remote terminal, but still may be transmitted to the end user in wires adjacent to DSL signals transmitted from a more distant source, such as the central office.
Interference introduces noise and effectively reduces the transmission rate for a DSL signal. A first DSL signal of two DSL signals may be associated with spectrum management standards restricting the amount of interference the second DSL signal can introduce to the first DSL signal. Generally, a DSL signal will cause more interference to another DSL signal of the same frequency when transmitted at a higher power level than a lower power level. This interference may be within acceptable levels as dictated by the spectrum management standards when the first and second DSL signals are of equal power levels or the first has a higher power level than the second DSL signal. If the first DSL signal does not have a higher power level, crosstalk may be above levels acceptable by the standards. If the second DSL signal having a cabinet as its source share the same frequencies as the first DSL signal having a more distant source, there is a risk that the second DSL signal will have a higher power level than the first DSL signal and may cause unacceptable levels of crosstalk for the first DSL signal.
Prior art methods determine power levels of DSL signals to minimize crosstalk by using a minimally acceptable power level for such a second DSL signal. However, as lower frequencies are capable of transmitting more data than higher frequencies because of lesser attenuation, it is preferable to have the power level of the second DSL signal as high as possible while keeping crosstalk from the second DSL signal to the first DSL signal within acceptable standards.
There is a need for a system and method to increase power levels of a DSL signal while keeping crosstalk from the DSL signal to other DSL signals within acceptable standards.